# A student is investigating the effect of temperature on the rate of enzyme activity using a colorimeter. Explain why it is important that the student zeroes (blanks) the colorimeter with a cuvette containing only the buffer solution before taking absorbance readings from the enzyme-substrate mixture.

> OCR A-Level Biology A (H420) — 1.2 Practical skills assessed in the practical endorsement · Explain · 4 marks

> A student sets up an investigation in which a coloured product is produced when an enzyme acts on a colourless substrate dissolved in a phosphate buffer. The student uses a colorimeter to measure absorbance at regular intervals to track the rate of reaction at different temperatures.

## Mark scheme (4 marks)

1. Blanking removes the absorbance contribution of the buffer solution itself (or the cuvette/solvent)
2. This ensures that only the absorbance due to the coloured product is measured (not the background)
3. This allows valid comparisons between readings taken at different temperatures (controls a variable)
4. Without blanking, any absorbance by the buffer would cause the calculated rate to be an overestimate (or readings would not be zero at time zero)

## Key terms

- [colorimeter](https://www.gradenine.co.uk/glossary/colorimeter)
- [absorbance](https://www.gradenine.co.uk/glossary/absorbance)
- [buffer solution](https://www.gradenine.co.uk/glossary/buffer-solution)
- [cuvette](https://www.gradenine.co.uk/glossary/cuvette)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-investigating-the-effect-3529ed75) · Published by Druglandscape Ltd.